Its even worse when you force Firefox to use wayland its icon doesn't even show.
Edit: Oh since everyone now is confused; I only have the flatpak version of Firefox installed yet it doesn't use the pinned icon and doesn't even use the firefox icon under wayland at all.
Am a developer and I can very much agree on package managers have nasty configuration, but at the same time flatpak is the exact same thing. No different that any other package. Except now you have to learn yet another standard that's even less popular than major ones. You can even claim it's easier, but the fact remains it's not the defacto standard, so you still have to provide other packages as well as flatpak if you wish to do so.